... and what can be done about it
Many successful WordPress site owners have moved their sites over to WPEngine for their high performance and high speed even under very heavy traffic.
WP Engine is able to provide this kind of speed thanks to their "hand-built a WordPress-specific EverCache system" and "a fully-managed CDN service" (for more info see WP Engine's articles on speed and infrastructure).
Keep reading Why WPEngine caching doesn't work with eCommerce sites